Nov 6, 2015 05:56 PM
Snowball Earth, by Gabrielle Walker: A Review
https://bibliomaneblog.wordpress.com/201...-a-review/
EXCERPT: A good, solidly written book with no major flaws of composition, "Snowball Earth" tells the story of Paul Hoffman, an irascible geologist behind a new theory of the role played by geology and climate to kickstart the development of complex life on Earth. Geology is a discipline that describes “deep time,” filled ages so vast and processes often so slow that the whole of human history is but the blink of an eye. [...] What the Snowball Earth hypothesis suggests is that a planet-wide ice age 700 million years ago put such stresses on life that evolution, which had previously just been mucking about with small, simple creatures, began to drive a change whereby larger, multicellular entities had a survival advantage. This, it is suggested, drove the evolution of a complex array of multicellular creatures...
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Climate change is moving mountains: Research points to strong interaction between climate shifts, increased internal movement in the North American St. Elias Mountain Range
http://www.sciencedaily.com/releases/201...121523.htm
RELEASE: For millions of years global climate change has altered the structure and internal movement of mountain ranges, but the resulting glacial development and erosion can in turn change a mountain's local climate. The degree of this cause-and-effect relationship has never been clearly observed, until now.
Based on research led by University of Cincinnati geologist Eva Enkelmann in the St. Elias Mountain Range -- located along the Pacific coastal region of North America -- the way a mountain range moves and behaves topographically can also change and create its local climate by redirecting wind and precipitation. The repercussions of these changes can in turn, accelerate the erosion and tectonic seismic activity of that mountain range.
Based on her findings, Enkelmann shows clear evidence for a strong relationship between global and local climate change and a mountain's internal tectonic plate shifts and topographic changes.
Enkelmann, an assistant professor in the University of Cincinnati Department of Geology, was among several UC researchers and thousands of geoscientists from around the globe presenting their findings at the 2015 Annual Geological Society of America Meeting, Nov.1-4, in Baltimore.
This research also was published in July in the journal Geophysical Research Letters.
"To understanding how mountain structures evolve through geologic time is no quick task because we are talking millions of years," says Enkelmann. "There are two primary processes that result in the building and eroding of mountains and those processes are interacting."
Looking at the St. Elias Mountains in particular, Enkelmann notes how dry it is in the northern part of the mountain range. But the precipitation is very high in the southern area, resulting in more erosion and material coming off the southern flanks. So as the climate change influences the erosion, that can produce a shift in the tectonics. This has been suggested in earlier studies based on numerical and analytical models, however, it had not yet been shown to have occurred over geologic times in the real world.
Enkelmann synthesized several different data sets to show how a rapid exhumation occurred in the central part of the mountain range over four to two million years ago. This feedback process between erosion and internal tectonic shifting resulted in a mass of material moving up toward the surface very rapidly.
Enkelmann's model suggests that global climate shifts triggered a change in the rheology -- the way material behaves.
While Earth was much warmer millions of years ago, glaciers still existed in the high altitudes. However, 2.6 million years ago Earth experienced a shift to a colder climate and glaciation intensified. Existing glaciers grew larger, froze solid, covered the area and did not move.
Enkelmann says the glaciers today are wet-based and are moving, very aggressively eroding material around and out, and in the case of her observation, into the Gulf of Alaska. The tectonic forces (internal plates moving toward one another) continue to move toward Alaska, get pushed underneath and the sediment on top is piling up above the Yakutat plate.
Adding to the already complex effects of climate change, these processes essentially work against each other.
The movement of glaciers can compete with the internal buildup and develop a feedback process that is very rapid and ferocious. Scientists have suggested that the Himalayas, European Alps and mountains in Taiwan were caused by the same competing reactions as those Enkelmann has observed in southeastern Alaska.
In Enkelmann's observation, the climate-driven erosion can influence the tectonics and change the motion of the rocks in that area. This makes studying the St. Elias Mountain Range particularly ideal because this area is very active tectonically, with strong glacial erosion. As an example, she cites the Great Alaskan Earthquake of 1964 -- the world's second largest earthquake recorded to date -- that also resulted in a tsunami.
"In 1899, there were two big earthquakes in a row, an 8.1 and an 8.2 magnitude, says Enkelmann pointing to a photo of the resulting shoreline lift that still stands today. "These earthquakes resulted in up to 14 meters of co-seismic uplift on the shore, so the shoreline basically popped up 14 meters (45 feet) and it happened immediately.
"Our biggest concern today is the continued potential for earthquakes that can also result in tsunamis," says Enkelmann.
Enkelmann appreciates the challenge of collecting samples here because this range has the highest peaks of any coastal mountain range and is only 20 kilometers from the Pacific Ocean, but she points out that it is a tough area to study because of the big ice sheets.
"So as geologists, we go to the area and take samples and do measurements in the field on the mountain ranges that stick out," says Enkelmann. "One approach is to sample the material that comes out of the glaciers that has transported the eroded sediment and analyze that sediment.
"By going to all of these individual glaciers, we can get a much better understanding of what has happened and what was moved on the entire mountain range."
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Supervolcanoes likely triggered externally
http://www.sciencedaily.com/releases/201...151534.htm
RELEASE: Supervolcanoes, massive eruptions with potential global consequences, appear not to follow the conventional volcano mechanics of internal pressure building until the volcano blows. Instead, a new study finds, such massive magma chambers might erupt when the roof above them cracks or collapses.
Knowledge of triggering mechanisms is crucial for monitoring supervolcano systems, including ones that lie beneath Yellowstone National Park and Long Valley, California, according to the study led by Patricia Gregg, University of Illinois professor of geology, in collaboration with professor Eric Grosfils of Pomona College and professor Shan de Silva of Oregon State University. The study was published in the Journal of Volcanology and Geothermal Research. Gregg also presented the findings this week at the annual meeting of the Geological Society of America.
"If we want to monitor supervolcanoes to determine if one is progressing toward eruption, we need better understanding of what triggers a supereruption," Gregg said. "It's very likely that supereruptions must be triggered by an external mechanism and not an internal mechanism, which makes them very different from the typical, smaller volcanoes that we monitor."
A supervolcano is classed as more than 500 cubic kilometers of erupted magma volume. For comparison, Gregg said, Mount St. Helen's ejected about one cubic kilometer of material, so a supervolcano is more than five hundred times larger.
"A typical volcano, when it erupts, can have lasting impacts across the globe," Gregg said. "We've seen that in Iceland when we've had large ash eruptions that have completely disrupted air traffic across Europe. A supereruption takes that to the nth degree."
The new study's findings are contrary to a pair of papers published in the journal Nature Geoscience in 2014 that claim a link between eruption likelihood and magma buoyancy. The magma byouancy hypothesis suggested that magma may be less dense than the rock surrounding it and therefore could push up against the roof, like an ice cube bobbing in water, increasing the pressure within the chamber and triggering an eruption.
"Typically, when we think about how a volcanic eruption is triggered, we are taught that the pressure in the magma chamber increases until it causes an explosion and the volcano erupts," Gregg said. "This is the prevailing hypothesis for how eruptions are triggered. At supervolcanic sites, however, we don't see a lot of evidence for pressurization. When I incorporated buoyancy into my numerical models, I couldn't reproduce the 2014 studies."
Gregg's numerical model incorporates all of the physics -- conserving mass, energy and momentum -- to calculate what would happen if a large buoyant magma body were to form in the shallow crust. The model showed that even when the chamber was huge and the difference in density was very large between the magma and he surrounding rock -- an unlikely scenario -- buoyancy added very little pressure to the system.
"The fact that my numerical model was not agreeing with their analytical solution suggested that there was something missing from the analytical solution. So that prompted me to look closer," Gregg said. "What they miss in the buoyancy model is Newtonian physics: The magma may push up, but the roof pushes back down."
The new study found that the size of the magma chamber is a much greater factor in generating supervolcanic eruptions. The buoyancy studies suggested that this correlation was due to having more material pushing up, but the Illinois-led study found that the size of the chamber affects the stability of the rock containing the chamber.
"Previous studies have found that as a magma chamber expands, it pushes the roof up and forms faults," Gregg said. "As these very large magma chambers grow, the roof above may become unstable and it becomes easier to trigger an eruption through faulting or failure within the rock. "
According to the model, if a crack or fault in the roof penetrates the magma chamber, the magma uses the crack as a vent to shoot to the surface. This could trigger a chain reaction that "unzips" the whole supervolcano.
Next, Gregg's group hopes to take advantage of the advanced computing facilities available at the University of Illinois, such as the Blue Waters supercomputer at the National Center for Supercomputing Applications. The researchers are working to create 4-D models that track the evolution of the Long Valley magma chamber over time in greater detail.
"If we see a correlation between magma chamber size and the ability to erupt, it is important to know if supervolcano eruptions are triggered by internal factors or by foundering and faulting in the roof. It may mean that we have to monitor these volcanoes differently," Gregg said. "If the trigger is an external force, whether it be an earthquake or a fault, then we should look at seismicity, what types of faults are being developed, what is the stability of the roof, and what kinds of activities are happening on the surface that could cause faulting."
https://bibliomaneblog.wordpress.com/201...-a-review/
EXCERPT: A good, solidly written book with no major flaws of composition, "Snowball Earth" tells the story of Paul Hoffman, an irascible geologist behind a new theory of the role played by geology and climate to kickstart the development of complex life on Earth. Geology is a discipline that describes “deep time,” filled ages so vast and processes often so slow that the whole of human history is but the blink of an eye. [...] What the Snowball Earth hypothesis suggests is that a planet-wide ice age 700 million years ago put such stresses on life that evolution, which had previously just been mucking about with small, simple creatures, began to drive a change whereby larger, multicellular entities had a survival advantage. This, it is suggested, drove the evolution of a complex array of multicellular creatures...
- - - - - - - -
Climate change is moving mountains: Research points to strong interaction between climate shifts, increased internal movement in the North American St. Elias Mountain Range
http://www.sciencedaily.com/releases/201...121523.htm
RELEASE: For millions of years global climate change has altered the structure and internal movement of mountain ranges, but the resulting glacial development and erosion can in turn change a mountain's local climate. The degree of this cause-and-effect relationship has never been clearly observed, until now.
Based on research led by University of Cincinnati geologist Eva Enkelmann in the St. Elias Mountain Range -- located along the Pacific coastal region of North America -- the way a mountain range moves and behaves topographically can also change and create its local climate by redirecting wind and precipitation. The repercussions of these changes can in turn, accelerate the erosion and tectonic seismic activity of that mountain range.
Based on her findings, Enkelmann shows clear evidence for a strong relationship between global and local climate change and a mountain's internal tectonic plate shifts and topographic changes.
Enkelmann, an assistant professor in the University of Cincinnati Department of Geology, was among several UC researchers and thousands of geoscientists from around the globe presenting their findings at the 2015 Annual Geological Society of America Meeting, Nov.1-4, in Baltimore.
This research also was published in July in the journal Geophysical Research Letters.
"To understanding how mountain structures evolve through geologic time is no quick task because we are talking millions of years," says Enkelmann. "There are two primary processes that result in the building and eroding of mountains and those processes are interacting."
Looking at the St. Elias Mountains in particular, Enkelmann notes how dry it is in the northern part of the mountain range. But the precipitation is very high in the southern area, resulting in more erosion and material coming off the southern flanks. So as the climate change influences the erosion, that can produce a shift in the tectonics. This has been suggested in earlier studies based on numerical and analytical models, however, it had not yet been shown to have occurred over geologic times in the real world.
Enkelmann synthesized several different data sets to show how a rapid exhumation occurred in the central part of the mountain range over four to two million years ago. This feedback process between erosion and internal tectonic shifting resulted in a mass of material moving up toward the surface very rapidly.
Enkelmann's model suggests that global climate shifts triggered a change in the rheology -- the way material behaves.
While Earth was much warmer millions of years ago, glaciers still existed in the high altitudes. However, 2.6 million years ago Earth experienced a shift to a colder climate and glaciation intensified. Existing glaciers grew larger, froze solid, covered the area and did not move.
Enkelmann says the glaciers today are wet-based and are moving, very aggressively eroding material around and out, and in the case of her observation, into the Gulf of Alaska. The tectonic forces (internal plates moving toward one another) continue to move toward Alaska, get pushed underneath and the sediment on top is piling up above the Yakutat plate.
Adding to the already complex effects of climate change, these processes essentially work against each other.
The movement of glaciers can compete with the internal buildup and develop a feedback process that is very rapid and ferocious. Scientists have suggested that the Himalayas, European Alps and mountains in Taiwan were caused by the same competing reactions as those Enkelmann has observed in southeastern Alaska.
In Enkelmann's observation, the climate-driven erosion can influence the tectonics and change the motion of the rocks in that area. This makes studying the St. Elias Mountain Range particularly ideal because this area is very active tectonically, with strong glacial erosion. As an example, she cites the Great Alaskan Earthquake of 1964 -- the world's second largest earthquake recorded to date -- that also resulted in a tsunami.
"In 1899, there were two big earthquakes in a row, an 8.1 and an 8.2 magnitude, says Enkelmann pointing to a photo of the resulting shoreline lift that still stands today. "These earthquakes resulted in up to 14 meters of co-seismic uplift on the shore, so the shoreline basically popped up 14 meters (45 feet) and it happened immediately.
"Our biggest concern today is the continued potential for earthquakes that can also result in tsunamis," says Enkelmann.
Enkelmann appreciates the challenge of collecting samples here because this range has the highest peaks of any coastal mountain range and is only 20 kilometers from the Pacific Ocean, but she points out that it is a tough area to study because of the big ice sheets.
"So as geologists, we go to the area and take samples and do measurements in the field on the mountain ranges that stick out," says Enkelmann. "One approach is to sample the material that comes out of the glaciers that has transported the eroded sediment and analyze that sediment.
"By going to all of these individual glaciers, we can get a much better understanding of what has happened and what was moved on the entire mountain range."
- - - - - - - -
Supervolcanoes likely triggered externally
http://www.sciencedaily.com/releases/201...151534.htm
RELEASE: Supervolcanoes, massive eruptions with potential global consequences, appear not to follow the conventional volcano mechanics of internal pressure building until the volcano blows. Instead, a new study finds, such massive magma chambers might erupt when the roof above them cracks or collapses.
Knowledge of triggering mechanisms is crucial for monitoring supervolcano systems, including ones that lie beneath Yellowstone National Park and Long Valley, California, according to the study led by Patricia Gregg, University of Illinois professor of geology, in collaboration with professor Eric Grosfils of Pomona College and professor Shan de Silva of Oregon State University. The study was published in the Journal of Volcanology and Geothermal Research. Gregg also presented the findings this week at the annual meeting of the Geological Society of America.
"If we want to monitor supervolcanoes to determine if one is progressing toward eruption, we need better understanding of what triggers a supereruption," Gregg said. "It's very likely that supereruptions must be triggered by an external mechanism and not an internal mechanism, which makes them very different from the typical, smaller volcanoes that we monitor."
A supervolcano is classed as more than 500 cubic kilometers of erupted magma volume. For comparison, Gregg said, Mount St. Helen's ejected about one cubic kilometer of material, so a supervolcano is more than five hundred times larger.
"A typical volcano, when it erupts, can have lasting impacts across the globe," Gregg said. "We've seen that in Iceland when we've had large ash eruptions that have completely disrupted air traffic across Europe. A supereruption takes that to the nth degree."
The new study's findings are contrary to a pair of papers published in the journal Nature Geoscience in 2014 that claim a link between eruption likelihood and magma buoyancy. The magma byouancy hypothesis suggested that magma may be less dense than the rock surrounding it and therefore could push up against the roof, like an ice cube bobbing in water, increasing the pressure within the chamber and triggering an eruption.
"Typically, when we think about how a volcanic eruption is triggered, we are taught that the pressure in the magma chamber increases until it causes an explosion and the volcano erupts," Gregg said. "This is the prevailing hypothesis for how eruptions are triggered. At supervolcanic sites, however, we don't see a lot of evidence for pressurization. When I incorporated buoyancy into my numerical models, I couldn't reproduce the 2014 studies."
Gregg's numerical model incorporates all of the physics -- conserving mass, energy and momentum -- to calculate what would happen if a large buoyant magma body were to form in the shallow crust. The model showed that even when the chamber was huge and the difference in density was very large between the magma and he surrounding rock -- an unlikely scenario -- buoyancy added very little pressure to the system.
"The fact that my numerical model was not agreeing with their analytical solution suggested that there was something missing from the analytical solution. So that prompted me to look closer," Gregg said. "What they miss in the buoyancy model is Newtonian physics: The magma may push up, but the roof pushes back down."
The new study found that the size of the magma chamber is a much greater factor in generating supervolcanic eruptions. The buoyancy studies suggested that this correlation was due to having more material pushing up, but the Illinois-led study found that the size of the chamber affects the stability of the rock containing the chamber.
"Previous studies have found that as a magma chamber expands, it pushes the roof up and forms faults," Gregg said. "As these very large magma chambers grow, the roof above may become unstable and it becomes easier to trigger an eruption through faulting or failure within the rock. "
According to the model, if a crack or fault in the roof penetrates the magma chamber, the magma uses the crack as a vent to shoot to the surface. This could trigger a chain reaction that "unzips" the whole supervolcano.
Next, Gregg's group hopes to take advantage of the advanced computing facilities available at the University of Illinois, such as the Blue Waters supercomputer at the National Center for Supercomputing Applications. The researchers are working to create 4-D models that track the evolution of the Long Valley magma chamber over time in greater detail.
"If we see a correlation between magma chamber size and the ability to erupt, it is important to know if supervolcano eruptions are triggered by internal factors or by foundering and faulting in the roof. It may mean that we have to monitor these volcanoes differently," Gregg said. "If the trigger is an external force, whether it be an earthquake or a fault, then we should look at seismicity, what types of faults are being developed, what is the stability of the roof, and what kinds of activities are happening on the surface that could cause faulting."